[{Shore Leave}] is the only episode in which the U.S.S. Enterprise is seen orbiting a planet from right to left. The I.S.S. Enterprise also does this briefly in the parallel universe, in the teaser to {Mirror, Mirror}, but by the beginning of Act I, it is again orbiting from left to right.

Actor Mark Lenard, best known for his role as Sarek, Spock's father, was the first actor to play a member of all three of the major alien races: Romulan, Vulcan, and Klingon (he is the commander of the Klingon attack group at the beginning of Star Trek: The Motion Picture.

James Doohan ("Scotty") lost his right middle finger during WWII. Most of his scenes are shot to hide it. However, it is very noticeable in the episode {Catspaw}. Scotty is hypnotized and holding a phaser pistol on Kirk & Spock in Korob & Sylvia's dining hall. When Scotty is in the shot, only two fingers are holding the butt of the phaser.

The slanting crawlway that leads up to the warp-drive nacelles is referred to as a "Jefferies tube." This is a reference to art director [?] Walter M. Jefferies.

After viewing the popularity of characters such as Robin on the [Batman] series and shows like [The Monkees], the producers decided to introduce Ensign Pavel Chekov in the second season in order to attract more teenage viewers, especially girls, to the show. Walter Koenig was selected due to his resemblance to [?] Davy Jones.

In {Catspaw}, the alien voices of the revealed forms of Sylvia and Korob are actually the sounds made by newly-hatched alligators calling for their mother.

The series' opening credits has lyrics that were never used (although they were published in the book The Making of Star Trek, by [?] Stephen A. Whitfield). They were written by Gene Roddenberry so that he would receive a residual for the theme's use alongside the theme's composer, Alexander Courage.

{A Piece Of The Action} is the only episode in which the Enterprise phasers are used to stun.

The episode {Assignment: Earth} was written to introduce a hoped-for spin-off series that never materialized. It would have featured Robert Lansing as Gary Seven, Victoria Vetri as Isis, and Teri Garr as Roberta Lincoln. In the new series, the intrepid three would have worked to make sure humanity achieved the destiny glimpsed via the Trek characters and Seven's mysterious extraterrestrial information. While the series never made it to television, it has become a comic book series.